Comparison of Sm complexes with Sn compounds for syntheses of copolymers composed of lactide and cyclic carbonates and their biodegradabilities

The comparison of organolanthanide complexes, (C5Me5)2SmMe(THF) (Sm1) and [(C5Me5)2Sm]2(PhC=C=C= CPh) (Sm2), with tin compounds, Bu2Sn(OMe)2 (Sn1) and Bu2Sn(OCH2CH2CH2O) (Sn2), in the preparation of random, diblock, and triblock copolymers composed of L-lactide (L-LA) or D,L-LA and cyclic carbonates, trimethylene carbonate (TMC) or 2,2-dimethyltrimethylene carbonate (DTC) is reported. The biodegradabilities of the resulting copolymers with proteinase K and a compost were examined. The copolymerization of L-LA with cyclic carbonates by Sm1 or Sm2 afforded copolymers with relatively low melting points (<160 °C) due to the accompanying epimerization in comparison with those obtained with Sn1 or Sn2. In the degradation of the polymers with a compost, the copolymers based on D,L-LA were more degradable than those based on L-LA. On the other hand, the effect of the incorporated cyclic carbonate on its degradability was more drastic in the copolymers based on L-LA than those in the copolymers based on D,L-LA. The introduction of only a small amount of the cyclic carbonates into PLLA significantly enhanced the degradability of PLLA with a compost or proteinase K. In the enzymatic degradation of L-LA-containing polymers, the copolymerization of L-LA with TMC was also quite effective to improve the degradability of PLLA. Triblock copolymerization tends to be effective to enhance the degradability of PLLA.